1. Field of the Invention
This invention relates generally to transcutaneous measurement of partial pressure of oxygen and relates particularly to the use of 2-thenoyltrifluoroacetone as a topical agent for improving such measurements.
2. Description of the Prior Art
Transcutaneous oxygen monitors are available commercially (cf. TCM 2 by Radiometer A/S, Copenhagen, Denmark, TCO.sub.2 M by Novametrix Medical Systems, Inc., Wallingford, Conn. 06492 and OXYMONITOR by Litton Medical Electronics, Elk Grove Village, Ill. 60007). These monitors utilize a sensor unit which is applied to the skin of a person whose transcutaneous partial pressure of oxygen is to be measured. The sensor unit generally comprises a barrier such as a membrane permeable to oxygen. Oxygen diffuses through the membrance and into an electrolyte solution stored on the electrode side of the membrane and in which oxygen is soluble. An electrode assembly in contact with the electrolyte solution measures the concentration of oxygen dissolved in the electrolyte solution, thus providing a measurement of the amount of oxygen diffusing through the skin. Alternative sensor units measure the quantity of oxygen diffusing through the skin without the use of membranes. Further alternatives perform such measurements without the use of electrodes.
Transcutaneous oxygen monitors are currently used in monitoring the transcutaneous partial pressure of oxygen in the prematurely born, both to guide treatment where supplemental oxygen is being administered and to assist in diagnosis where there is a question about the blood oxygen level. The transcutaneous partial pressure of oxygen and the diffusion of oxygen through the skin respond rapidly to changes in the concentration of inspired oxygen. Transcutaneous oxygen monitors are thus used frequently in treatment and diagnosis since too much oxygen can cause damage to a baby's retina and too little oxygen can cause brain damage.
The partial pressure of oxygen over the surface of skin does not correlate well with arterial partial pressure at normal skin temperatures. It is common to heat the skin by heating elements located in the sensor unit. Heating the skin in this manner has resulted in an acceptable correlation between arterial and transcutaneous partial pressures of oxygen in newborns. However, the recommended electrode temperature for newborns of 44.degree. C. can produce thermal injury to skin after several hours. In an effort to reduce such thermal injury, sensor units are routinely relocated to a virgin patch of skin every several hours.
Transcutaneous oxygen monitors are also used in monitoring the transcutaneous partial pressure of oxygen in the diagnosis and treatment of various diseases in children and adults. The approach of heating the skin, even to an electrode temperature of 45.degree. C., has not generally yielded an acceptable correlation between arterial and transcutaneous partial pressures of oxygen in children and adults.
It is an object of the present invention to reduce thermal injury to skin caused by heating the skin and to improve the correlation between arterial and transcutaneous partial pressures of oxygen. In particular it is an object of the present invention to achieve an acceptable correlation of arterial and transcutaneous partial pressures while using lower skin temperatures. It is an object to reduce thermal injury to skin and reduce the frequency with which sensor units must be relocated to virgin patches of skin. It is an object to achieve an acceptable correlation of arterial and transcutaneous partial pressures in adults as well as newborns.